Micro-wave tube with mechanical frequency tuning

ABSTRACT

This invention relates to a microwave tube ( 3 ) for generation of an electromagnetic wave with frequency F, the tube comprises mechanical means for varying the frequency F composed of a set of rings (A, B, C, D) defining a periodic structure inside the tube and mechanical means ( 4, 5, 2,  G) for displacing rings with respect to each other while maintaining a periodicity for periodic structure during displacement of the rings.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority based on International PatentApplication No. PCT/FR03/01960, entitled “Microwave Tube With MechanicalFrequency Tuning” by Jehan VANPOPERYNGHE and Jean-Paul PRULHIERE, whichclaims priority of French Application No. 02 07849, filed on Jun. 25,2002, which was not published in English.

TECHNICAL DOMAIN AND PRIOR ART

The invention relates to a microwave tube with mechanical frequencytuning.

The invention is used in a particularly advantageous application in thedomain of electronic tubes for generating and/or amplifying radioelectric signals.

The principle of a microwave tube according to known art is shown inFIG. 1. The microwave tube comprises:

-   -   a source of electrons composed of an emission cathode K and an        anode electron gun CA to form an electron beam F,    -   a focusing coil L surrounding the electron beam and producing a        continuous axial magnetic field B so as to prevent the electron        beam expansion by mutual repulsion between electrons,    -   a microwave structure H placed close to the beam and capable of        generating, propagating and amplifying an electromagnetic wave,        and    -   a collector C to collect electrons after interaction with the        wave.

Many families of tubes apply the operating principle described above,for example progressive wave tubes (PWT), BackWard Oscillators (BWO)type tubes, klystrons, magnetrons, carcinotrons, masers, etc.

These tubes can operate in single pulse mode or in recurrent mode (pulsestream).

To provide very high powers, designers use periodic structures and/orcavities that can give strong amplifications. Among these structures,there are BWO type tubes for which the schematic diagram is given inFIG. 2. A BWO type tube comprises an insert I and a periodic structureP. A distance d defines the period of the periodic structure. A BWO typemicrowave tube is optimised for a single frequency F. Therefore, it isonly efficient within a very narrow frequency band ΔF, and particularlynarrow when the output power is high (typically ΔF/F<5%).

In general, the microwave tubes mentioned above are optimised to work ata fixed frequency and known means of varying the frequency of the tubealways cause a severe degradation of tube performances.

The invention does not have this disadvantage.

SUMMARY OF THE INVENTION

The invention relates to a microwave tube for generation of anelectromagnetic wave with frequency F, characterised in that itcomprises mechanical means for varying the frequency F composed of a setof rings defining a periodic structure inside the tube, and mechanicalmeans for displacing rings with respect to each other while maintaininga periodicity for the periodic structure during displacement of therings.

According to a first embodiment of the invention, the mechanical meansfor displacing the rings comprise a set of electrical contacts betweenrings, at least one lead screw, a set of nuts installed on the leadscrew, a set of rods, each rod firmly connecting a nut to a ring, thetube being provided with at least one slit enabling rods to pass in thewall of the tube, the lead screw comprising several sectors withdifferent pitches capable of keeping intervals between the rings duringrotation of the lead screw.

According to a second embodiment of the invention, the mechanical meansfor displacing rings comprise a set of electrical contacts between therings, at least one set of pins, each pin being firmly connected to aring, the tube being provided with at least one longitudinal slitthrough which pins can pass in the wall of the tube, a ring external tothe tube comprising at least one set of slits, each slit in the outerring allowing the passage of at least one pin, the slits in a set ofslits having a different inclination for each ring so as to maintain aperiodicity for the different rings during displacement of the rings.

Therefore advantageously, regardless of the embodiment of the invention,the mechanical means for varying the frequency F include at least onelongitudinal slit formed in the tube and allowing the passage of meansof entraining all rings.

According to another characteristic, the microwave tube according to theinvention is a PWT, a BWO type tube, a carcinotron, or a maser.

According to yet another characteristic of the invention, the periodicstructure of the microwave is corrugated plate.

The invention has the advantage that the frequency F of the emittedelectromagnetic wave can be varied within a large variation range,namely a few tens of percent, while maintaining amplificationperformances of the electromagnetic wave existing in the power sourcesworking at fixed frequency.

The invention is advantageously applicable to any radio-electric powersource composed of a beam of electrons circulating through a structurecomprising periodic or non-periodic variations.

The integrated source according to the invention comprises a periodiccorrugated geometric structure to enable a frequency variation using amechanical process enabling either a modification of the pitch of theperiodic structure, for example composed of a corrugated plate, or avariation of the length of an insert, or a combination of bothstructures.

Advantageously, this integrated system enables fast modulation ofparameters, namely the frequency and power of the radio frequencysignal. The system can easily be automated and can be quickly externallycontrolled without needing to modify operation of the electron beam.

This integrated system can be particularly well adapted to BWO typehyper frequency tubes. It then replaces periodic structures in placeand/or inserts. It is also easily adaptable to other types of tubes. Itmay also be associated with other systems provided to enable variationof the output frequency of the signal. It can then advantageously beused to increase the efficiency and the operating range of the system.

The frequency radiated by a tube according to the invention mayadvantageously be chosen in a significant range, for example severaltens of percent, without reducing the output power, other tubeparameters (for example such as the voltage and current of the electronbeam) being unchanged.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will becomeclearer after reading a preferred embodiment with reference to theappended figures, wherein:

FIG. 1 shows a schematic diagram of the microwave tube according toknown art;

FIG. 2 shows a schematic diagram of the BWO tube according to known art;

FIGS. 3A and 3B represent a first embodiment of a microwave tubeaccording to the invention;

FIGS. 3C-3F represent enlarged parts of FIG. 3A;

FIGS. 4A and 4B represent a second embodiment of the microwave tubeaccording to the invention.

The same reference labels denote the same elements in all figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

A first embodiment of the invention is shown in FIGS. 3A and 3B.

The electromagnetic structure for adjustment of the frequency of themicrowave tube comprises a fixed part and a mobile part.

The fixed part is composed of the longitudinal wall 3 of the tube inwhich at least one guide slit G (FIG. 3B) is formed.

The mobile part comprises:

-   -   at least one lead screw 4,    -   nuts 5 installed on the lead screw 4,    -   a set of rods 6 and a set of rings (for example four rings A, B,        C, D), each rod 6 firmly fixing a nut to a ring, the rings being        installed on the inside of the wall 3 of the tube,    -   electrical contacts 2 (FIG. 3A) between the rings.

The guide slit(s) G enable passage of rods 6 in the longitudinal wall 3of the tube so as to connect the nuts 5 to the rings as best shown inFIG. 3B. A ring seen in section (see FIGS. 3A, 3B) may for example beprofiled like a rim.

During the frequency adjustment, the lead screw is moved in rotation,which drives the nuts 5, the rods 6, the rings A, B, C, D and theelectrical contacts 2 in a translation movement. According to onevariant of the first embodiment, the ring A may be connected to amechanical part p (FIG. 3A) that can then slide along tube 3.

The lead screw 4 is single piece. It is composed of several ranges ofdifferent threads adapted to each nut 5. A single lead screw istheoretically sufficient for use of the invention. As a non-limitativeexample, FIG. 3A illustrates the case in which the device comprises twolead screws. The second screw, when it is used, must then turn inperfect synchronism with the first lead screw. The quality oftranslation of the rings is improved due to symmetry of the movementapplication points.

A lead screw comprises several sectors with different pitches tomaintain the system at the same distance between the vertices of theperiodic corrugated structure formed by the rings, during rotation ofthe lead screw.

Let L(AB) be the distance between the rings A and B, L(BC) be thedistance between the rings B and C and L(CD) be the distance between therings C and D as best shown in FIG. 3A.

Let (a) be the pitch of the nut fixed to ring A as best shown in FIG.3C, (2 a) be the pitch of the nut fixed to ring B as best shown in FIG.3D,(3 a) be the pitch of the nut fixed to rim as best shown in FIG. 3E,(4 a) be the pitch of the nut fixed to ring D as best shown in FIG. 3F.

When the lead screw turns by 180°, ring A moves by (3.1416)×(a), ring Bmoves by (3.1416)×(2a), ring C moves by (3.1416)×(3a), and ring D movesby (3.1416)×(4a). The result is:L(AB)=(3.1416)(2a−a)=(3.1416)a,L(BC)=(3.1416)(3a−2a)=(3.1416)a,L(CD)=(3.1416)(4a−3a)=(3.1416)a.

Consequently:L(AB)=L(BC)=L(CD)=(3.1416)a,the periodicity of the structure is maintained. It varies linearly as afunction of the screw rotation.

FIGS. 4A and 4B show a second embodiment of the invention.

According to the second embodiment of the invention, the variation ofthe periodicity of the rings is based on the rotation of a ring equippedwith slits inside which pins connected to periodic corrugated structuresare able to move. The inclination of these slits is such that it enablesa specific interval to be maintained.

The tube 3 is the same as the tube in the previous assembly. Each ringA, B, C, D placed inside the tube 3 is fixed to a pin 7. A pin 7 movesinside two slits located on two independent parts, namely the fixed tube3 and an outer ring 8. A first slit 9 placed on the fixed tube 3 onlyenables ring translation movements in the longitudinal direction of thetube. A set of slits 10 placed on the outer ring 8 fixes the range ofvariations of the period of the periodic structure. They correspond tothe different pitches of the lead screw 4 of the previous assembly andperform the same function. The slits 10 (FIG. 4B) have a differentinclination for each ring so as to keep a specific periodicity at thedifferent rings, during displacement of the rings.

On the outer ring 8, there are as many pairs of slits 9, 10 and pins 7as the number of rings to be moved inside the tube 3.

Therefore, in this case the outer ring 8 may be compared with a set oflead screw/nut pairs in the device according to the first embodiment ofthe invention.

According to the embodiment shown in FIGS. 4A and 4B, the tube 3 onlycomprises a single longitudinal slit 9 and the outer ring 8 onlycomprises a single set of slits 10. The invention also relates to thecase in which the tube 3 comprises for example, two longitudinal slits9, the two longitudinal slits then being arranged symmetrically on thetube 3, and in which the outer ring then comprises two sets of slits 10,the second set of slits 10 being associated with the second longitudinalslit to displace the rings according to the principle of the invention.

Regardless of its embodiment, the mechanism according to the inventioncan be automated and controlled quickly from outside and at will withoutmodifying operation of the electron beam.

The two embodiments described above are given simply as examples. Anymechanical system that can quickly vary the position of the rings insidethe tube while maintaining the periodicity of the rings may also besuitable.

The two embodiments of the invention described above can easily becoupled to stepping motors, or to jacks placed either inside the tube oroutside the tube (movements then being made through sealed passages).The system according to the invention may be adapted to several sourcecategories, without affecting the basic principle.

According to one improvement of the invention, the microwave tube mayalso comprise an insert with an adjustable length. This type ofadjustment is implemented by displacement of a second tube in tube 3,keeping electrical continuity. This improvement is not used in itself tovary the frequency of the tube. For example, it can be used to adapt thetotal length of the tube (insert+periodic structure) to variations inthe length of the periodic structure.

1. A microwave tube for generation of an electromagnetic wave withfrequency F, the microwave tube comprising: mechanical means for varyingthe frequency F, wherein said mechanical means are composed of: a set ofrings defining a periodic structure inside the tube; and mechanicalmeans for displacing said set of rings with respect to each other whilemaintaining a periodicity for the periodic structure during displacementof the set of rings, wherein the mechanical means for displacing the setof rings comprises: a set of electrical contacts between the set ofrings; and one set of pins, each pin of said one set of pinsrespectively being firmly connected to a corresponding ring of the setof rings, the tube being provided with at least one longitudinal slitthrough which each one of the pins of the one set of pins can pass inthe wall of the tube, an outer ring external to the tube comprising aset of slits, each slit in the outer ring allowing the passage of acorresponding pin of the one set of pins, each slit in the set of slitshaving a different inclination for each corresponding ring of the set ofrings so as to maintain a periodicity for the different rings of the setof rings during displacement of the set of rings.
 2. A microwave tubefor generation of an electromagnetic wave with frequency F, themicrowave tube comprising: mechanical means for varying the frequency F,wherein said mechanical means are composed of: a set of rings defining aperiodic structure inside the tube; and mechanical means for displacingsaid set of rings with respect to each other while maintaining aperiodicity for the periodic structure during displacement of the set ofrings, wherein the mechanical means for displacing the set of ringscomprises: a set of electrical contacts between the set of rings; atleast one lead screw; a set of nuts installed on the at least one leadscrew; and a set of rods, each rod firmly connecting a respective one ofthe set of nuts to a corresponding one of the set of rings, the tubebeing provided with at least one slit enabling the set of rods to passin the wall of the tube, the at least one lead screw comprising severalsectors with different pitches capable of keeping intervals between theset of rings during rotation of the at least one lead screw.